Then, the website of respected Turkish daily Hurriyet said that an official Turkish source had confirmed to the paper that the plane was taken down by Syrian forces.

Another Lebanese media group, the pro-Iranian Al-Mayadeen television station, also said a Turkish plane was shot down off the Syrian coast, quoting the information from what it said was Turkish officials.

If the report is confirmed, it could represent a potential watershed moment in the ever-deteriorating relationship between former allies Turkey and Syria.

Moreover, since Turkey is a member of NATO, an unprovoked attack by Syria on its warplane could pose grave consequences for Damascus -- since an attack on one NATO member is considered, by the treaty that established the alliance, as an attack on the group as a whole.

Earlier, Turkish media reported that military officials lost radio contact with the missing aircraft off its southeastern coast and later said it crashed in the sea in Syria’s territorial waters.

CNN Turk TV noted that Ankara officials were staying in contact with their Syrian counterparts in order to search for the missing crewmen, who have not been found yet, according to Hurriyet.

Turkish Prime Minister Recep Tayyip Erdogan himself told the Haberturk paper that the Turkish pilots were alive and that Syrian defense forces even apologized for the incident. It is not clear if Erdogan believes the plane was shot down or that it crashed on its own.

“At this moment, the air force and navy are conducting search and rescue operations in the western Mediterranean, and luckily our pilots are alive; we have just lost a plane,” he told reporters while travelling back from a summit in Brazil.

Also according to Hurriyet, eyewitnesses in the northern Syrian town of Latakia told BBC Arabic that Syrian air defense shot down an unidentified aircraft near the town of Ras al-Baseet, close to the Turkish border.

The Turkish military said the plane was an American-made F-4E Phantom. Turkey flies an updated version of the Vietnam-era vintage U.S. fighter-bomber, which it calls the F-4E 2020 Terminator and modernized with the help of Israel. In Turkish service, the F-4 is employed mainly for reconnaissance and ground attack, although it is capable of being employed as an air-defense jet and taking down enemy planes.

Turkey and Syria, once friendly, have become bitter enemies.

Erdo?an has repeatedly condemned Assad for his brutal and horrific 15-month crackdown on opponents -- a campaign that has killed at least 14,000 people so far. Turkey has also allowed tens of thousands of Syrian refugees to take shelter in camps just across the border.